Synthesis and use of precursors for ALD of tellurium and selenium thin films

ABSTRACT

Atomic layer deposition (ALD) processes for forming Te-containing thin films, such as Sb—Te, Ge—Te, Ge—Sb—Te, Bi—Te, and Zn—Te thin films are provided. ALD processes are also provided for forming Se-containing thin films, such as Sb—Se, Ge—Se, Ge—Sb—Se, Bi—Se, and Zn—Se thin films are also provided. Te and Se precursors of the formula (Te,Se)(SiR 1 R 2 R 3 ) 2  are preferably used, wherein R 1 , R 2 , and R 3  are alkyl groups. Methods are also provided for synthesizing these Te and Se precursors. Methods are also provided for using the Te and Se thin films in phase change memory devices.

REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119(e) as adivisional of U.S. Non-Provisional application Ser. No. 12/429,133,filed Apr. 23, 2009 which in turn claims priority to U.S. ProvisionalApplication Nos. 61/048,077 filed Apr. 25, 2008; 61/112,128 filed Nov.6, 2008; and 61/117,896 filed Nov. 25, 2008, which are all herebyincorporated by reference in their entirety.

PARTIES OF JOINT RESEARCH AGREEMENT

The invention claimed herein was made by, or on behalf of, and/or inconnection with a joint research agreement between the University ofHelsinki and ASM Microchemistry signed on Nov. 14, 2003. The agreementwas in effect on and before the date the claimed invention was made, andthe claimed invention was made as a result of activities undertakenwithin the scope of the agreement.

BACKGROUND OF THE INVENTION

Field of the Invention

The present application relates generally to methods and compounds forforming thin films comprising tellurium (Te) or selenium (Se) by atomiclayer deposition. Such films may find use, for example, in phase changememory (PCM) devices and in optical storage media.

Description of the Related Art

Thin films comprising Te and Se are used in many different applications,including, for example, non-volatile phase-change memories (PCM), solarcells, and optical storage materials. The operation of PCM cells isbased on the resistivity difference between amorphous and crystallinestates of the active material. A resistivity difference of more thanthree orders of magnitude can be obtained by many different phase changealloys. The switching in a PCM cell is generally accomplished by heatingthe material locally with suitable current pulses, which, depending onthe intensity of the pulse, leave the material in a crystalline oramorphous state.

A wide variety of different PCM cell structures have been reported, manyof which use trench or pore-like structures. Sputtering has typicallybeen used in preparing PCM materials, but the more demanding cellstructures will require better conformality and more control of thedeposition process. Sputtering may be capable of forming simple pore andtrench structures, however, future PCM applications will require morecomplicated 3-D cell structures that cannot be formed using sputteringtechniques. Processes with greater precision and control, such as atomiclayer deposition (ALD), will be required to make these complicatedstructures. Using an atomic layer deposition process provides greaterprecision and control over the deposition, including better conformalityand better control of the composition of the deposited film.

Atomic layer deposition processes for depositing Te and Se-containingthin films have been limited, in part, by a lack of appropriateprecursors.

A need exists, therefore, for methods for controllably and reliablyforming thin films of phase change materials comprising tellurium andselenium by ALD.

SUMMARY OF THE INVENTION

The methods disclosed herein provide reliable atomic layer deposition(ALD) methods for forming thin films comprising tellurium and for makingprecursors that can be used in such methods.

In accordance with one aspect of the present invention, atomic layerdeposition processes for forming a Te or Se containing thin film areprovided. In some embodiments, the processes include a plurality ofdeposition cycles. In some embodiments, each deposition cycle comprises:providing a pulse of a first vapor phase reactant into the reactionchamber to form no more than about a single molecular layer of the firstreactant on the substrate; removing excess first reactant from thereaction chamber; providing a pulse of a second vapor phase Te or Sereactant to the reaction chamber such that the second vapor phasereactant reacts with the first reactant on the substrate to form Te orSe containing thin film, wherein the Te or Se reactant is Te(SiR¹R²R³)₂or Se(SiR¹R²R³)₂, wherein R¹, R², and R³ are alkyl groups with one ormore carbon atoms; and removing excess second reactant and reactionbyproducts, if any, from the reaction chamber.

In accordance with another aspect of the present invention, ALDprocesses for forming a Sb containing thin film on a substrate in areaction chamber are provided. The processes comprise a plurality ofdeposition cycles, each cycle comprising: providing a pulse of a firstvapor phase Sb reactant into the reaction chamber to form no more thanabout a single molecular layer of the Sb reactant on the substrate,wherein the Sb reactant comprises SbX₃, wherein X is a halogen; removingexcess first reactant from the reaction chamber; providing a pulse of asecond vapor phase reactant to the reaction chamber such that the secondvapor phase reactant reacts with the Sb reactant on the substrate toform a Sb containing thin film; and removing excess second reactant andreaction byproducts, if any, from the reaction chamber.

In accordance with another aspect of the present invention, ALDprocesses for forming a Ge containing thin film on a substrate in areaction chamber are provided. The processes comprising: providing afirst vapor phase reactant pulse comprising a Ge precursor into thereaction chamber to form no more than about a single molecular layer ofthe Ge precursor on the substrate, wherein the Ge precursor has aformula of GeX₂, wherein X are halides (F, Cl, Br or I); removing excessfirst reactant from the reaction chamber; providing a second vapor phasereactant pulse to the reaction chamber such that the second vapor phasereactant reacts with the Ge precursor on the substrate; removing excesssecond reactant and reaction byproducts, if any, from the reactionchamber; and repeating the providing and removing steps until a film ofa desired thickness is formed.

In accordance with another aspect of the present invention, ALDprocesses for forming a Te or Se containing thin film are provided. Theprocesses comprising: alternately and sequentially contacting asubstrate with a vapor phase reactant pulse comprising a first precursorand a vapor phase reactant pulse comprising a second precursorcomprising Te or Se, wherein the second precursor comprises Te or Sebound to two Si atoms; and repeating the alternate and sequential pulsesuntil a thin film of a desired thickness is obtained.

In accordance with another aspect of the present invention, processesfor making a Te or Se precursor are provided. The processes comprising:forming a first product by reacting a Group IA metal with a materialcomprising Te or Se; and subsequently adding a second reactantcomprising a silicon atom bound to a halogen atom, thereby forming acompound comprising Te or Se bound to two silicon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematic cross sections of various types of PCMstructures;

FIG. 2 is a flow chart generally illustrating a method for forming aSb—Te film in accordance with one embodiment;

FIG. 3 is a graph of the average deposited thickness of a Sb—Te film onsilicon with native oxide and on tungsten per cycle versus Te precursorpulse length;

FIG. 4 is a graph of the composition of a Sb—Te film on silicon withnative oxide as measured by energy dispersive x-ray (EDX) analysis;

FIG. 5 is a graph of the composition of a Sb—Te film on tungsten asmeasured by EDX analysis;

FIG. 6 is an x-ray diffractogram of a Sb—Te thin film on glass;

FIG. 7 is a flow chart generally illustrating a method for forming aGe—Te film in accordance with one embodiment;

FIG. 8 is a gracing incidence x-ray diffractogram of a Ge—Te thin filmon glass;

FIG. 9 is a flow chart generally illustrating a method for forming aGe—Sb—Te film in accordance with one embodiment;

FIG. 10 is a graph of the average deposited thickness of a Ge—Sb—Te filmper cycle versus Ge precursor pulse length;

FIG. 11 is a graph of the composition of a Ge—Sb—Te film as measured byEDX analysis;

FIG. 12 is a collection of x-ray diffractograms of several Ge—Sb—Te thinfilms on glass formed with varying Ge precursor pulse lengths;

FIG. 13 is a gracing incidence x-ray diffractogram of a Ge—Sb—Te thinfilm on glass;

FIG. 14 is a flow chart generally illustrating a method for forming aBi—Te film in accordance with one embodiment;

FIG. 15 is a gracing incidence x-ray diffractogram of a Bi—Te thin film;

FIG. 16 is a flow chart generally illustrating a method for forming aZn—Te film in accordance with one embodiment;

FIG. 17 is a gracing incidence x-ray diffractogram of a Zn—Te thin film;and

FIG. 18 is a flow chart generally illustrating a method for forming Teand Se precursors in accordance with one embodiment.

FIG. 19 is a graph of the composition of a Sb—Te thin film versus filmgrowth temperature.

FIG. 20 is a graph of the average growth rate per cycle of a Sb₂Te₃ thinfilm versus temperature on a tungsten substrate and a silicon substrate.

FIG. 21 is a graph of the growth rate per cycle of Sb₂Te₃ thin filmversus the pulse length of a Sb-precursor.

FIG. 22 is a graph of the growth rate per cycle of Sb₂Te₃ thin filmversus the pulse length of a Te-precursor.

FIG. 23 is a graph of the composition of a Ge—Sb—Te (GST) thin filmacross the surface of a substrate.

FIG. 24 is a graph of the average growth rate per cycle of a GST thinfilm versus the GeBr₂ precursor temperature.

FIG. 25 is a graph of the average growth rate per cycle of a GST thinfilm across the substrate surface for various GeBr₂ precursortemperatures.

FIG. 26 is a field emission scanning electron microscope (FESEM) imageof a GST thin film deposited in a high-aspect ratio trench pattern.

FIG. 27 is a gracing incidence X-ray diffractogram of a GST thin film.

FIGS. 28A+28B are graphs of the composition of GST thin films versusGeCl₂-dioxane precursor pulse length and versus Ge—Te cycling ratio,respectively.

FIG. 29 is a graph of the composition of a Cu—In—Se film as measured byenergy dispersive x-ray (EDX) analysis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As discussed above, Te and Se-containing films find use in a variety ofapplications, including phase change memory (PCM), solar cells, andoptical storage materials. PCM cells can have a variety of differentconfigurations. Typically, the PCM cell includes a transistor and aresistor between a top metal contact and a resistive bottom electrode.Additional PCM configurations are disclosed, for example, in “Phasechange memories: State-of-the-art, challenges and perspectives” byLacaita, Solid-State Electronics 50 (2006) 24-31, which is hereinincorporated by reference in its entirety. FIG. 1 illustrates threeschematic cross sections of configurations of PCM cells, including apillar cell, mushroom cell, and pore cell.

Solar cell absorber materials can comprise a variety of differentmaterials. Some of the most promising solar cell absorber materials areCuInSe₂-based chalcopyrite materials. CuSe_(x) also can be used in solarcells.

While the embodiments of the present invention are discussed in thegeneral context of PCM, the skilled artisan will appreciate that theprinciples and advantages taught herein will have application to otherdevices and applications. Furthermore, while a number of processes aredisclosed herein, one of ordinary skill in the art will recognize theutility of certain of the disclosed steps in the processes, even in theabsence of some of the other disclosed steps, and similarly thatsubsequent, prior and intervening steps can be added.

Antimony-telluride (including Sb—Te and Sb₂Te₃), Germanium-telluride(including GeTe), germanium-antimony-telluride (GST; Ge₂Sb₂Te₅),bismuth-telluride BiTe (including Bi₂Te₃), and zinc-telluride (includingZnTe) thin films can be deposited on a substrate by atomic layerdeposition (ALD) type processes. ALD type processes are based oncontrolled, self-limiting surface reactions of precursor chemicals. Gasphase reactions are avoided by feeding the precursors alternately andsequentially into the reaction chamber. Vapor phase reactants areseparated from each other in the reaction chamber, for example, byremoving excess reactants and/or reactant byproducts from the reactionchamber between reactant pulses.

Tellurium has several oxidation states, including −2, 0, +2, +4, and +6.Antimony has several oxidation states, including −3, +3, 0 and +5, ofwhich +3 is most common. A stoichiometric Sb—Te film with Te in a −2oxidation state comprises Sb₂Te₃. Germanium (Ge) has oxidation states of0, +2, and +4.

Tellurium (Te) compounds, where Te has an oxidation state of −2, aregenerally called tellurides. Tellurium compounds, where Te has anoxidation state of 0, are generally called tellurium compounds. However,for the sake of simplicity, as used herein thin films comprising Te arereferred to as tellurides. Thus films referred to as tellurides hereinmay contain Te with oxidations states other than −2, for example,oxidation states of 0, +2, +4, and +6. It will be apparent to theskilled artisan when a particular oxidation state is intended.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure.Deposition temperatures are maintained below the thermal decompositiontemperature of the reactants but at a high enough level to avoidcondensation of reactants and to provide the activation energy for thedesired surface reactions. Of course, the appropriate temperature windowfor any given ALD reaction will depend upon the surface termination andreactant species involved. Here, the temperature varies depending on thetype of film being deposited and is preferably at or below about 400°C., more preferably at or below about 200° C. and most preferably fromabout 20° C. to about 200° C.

A first reactant is conducted or pulsed into the chamber in the form ofa vapor phase pulse and contacted with the surface of the substrate.Conditions are preferably selected such that no more than about onemonolayer of the first reactant is adsorbed on the substrate surface ina self-limiting manner. The appropriate pulsing times can be readilydetermined by the skilled artisan based on the particular circumstances.Excess first reactant and reaction byproducts, if any, are removed fromthe reaction chamber, such as by purging with an inert gas.

Purging the reaction chamber means that vapor phase precursors and/orvapor phase byproducts are removed from the reaction chamber such as byevacuating the chamber with a vacuum pump and/or by replacing the gasinside the reactor with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 to 20 seconds, more preferably betweenabout 1 and 10, and still more preferably between about 1 and 2 seconds.However, other purge times can be utilized if necessary, such as wherehighly conformal step coverage over extremely high aspect ratiostructures or other structures with complex surface morphology isneeded.

A second gaseous reactant is pulsed into the chamber where it reactswith the first reactant bound to the surface. Excess second reactant andgaseous byproducts of the surface reaction, if any, are removed from thereaction chamber, preferably by purging with the aid of an inert gasand/or evacuation. The steps of pulsing and purging are repeated until athin film of the desired thickness has been formed on the substrate,with each cycle leaving no more than a molecular monolayer. Additionalphases comprising provision of a reactant and purging of the reactionspace can be included to form more complicated materials, such asternary materials.

As mentioned above, each pulse or phase of each cycle is preferablyself-limiting. An excess of reactant precursors is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage.

Removing excess reactants can include evacuating some of the contents ofthe reaction space and/or purging the reaction space with helium,nitrogen or another inert gas. In some embodiments purging can compriseturning off the flow of the reactive gas while continuing to flow aninert carrier gas to the reaction space.

The precursors employed in the ALD type processes may be solid, liquidor gaseous materials under standard conditions (room temperature andatmospheric pressure), provided that the precursors are in vapor phasebefore they are conducted into the reaction chamber and contacted withthe substrate surface, “Pulsing” a vaporized precursor onto thesubstrate means that the precursor vapor is conducted into the chamberfor a limited period of time. Typically, the pulsing time is from about0.05 to 10 seconds. However, depending on the substrate type and itssurface area, the pulsing time may be even higher than 10 seconds.Pulsing times can be on the order of minutes in some cases. The optimumpulsing time can be determined by the skilled artisan based on theparticular circumstances.

The mass flow rate of the precursors can also be determined by theskilled artisan. In some embodiments the flow rate of metal precursorsis preferably between about 1 and 1000 sccm without limitation, morepreferably between about 100 and 500 sccm.

The pressure in the reaction chamber is typically from about 0.01 toabout 20 mbar, more preferably from about 1 to about 10 mbar. However,in some cases the pressure will be higher or lower than this range, ascan be determined by the skilled artisan given the particularcircumstances.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature. The growth temperature variesdepending on the type of thin film formed, physical properties of theprecursors, etc. The growth temperatures are discussed in greater detailbelow in reference to each type of thin film formed. The growthtemperature can be less than the crystallization temperature for thedeposited materials such that an amorphous thin film is formed or it canbe above the crystallization temperature such that a crystalline thinfilm is formed. The preferred deposition temperature may vary dependingon a number of factors such as, and without limitation, the reactantprecursors, the pressure, flow rate, the arrangement of the reactor,crystallization temperature of the deposited thin film, and thecomposition of the substrate including the nature of the material to bedeposited on. The specific growth temperature may be selected by theskilled artisan.

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Pulsar® reactor andAdvance® 400 Series reactor, available from ASM America, Inc of Phoenix,Ariz. and ASM Europe B.V., Almere, Netherlands. In addition to these ALDreactors, many other kinds of reactors capable of ALD growth of thinfilms, including CVD reactors equipped with appropriate equipment andmeans for pulsing the precursors can be employed. Preferably, reactantsare kept separate until reaching the reaction chamber, such that sharedlines for the precursors are minimized. However, other arrangements arepossible, such as the use of a pre-reaction chamber as described in U.S.application Ser. No. 10/929,348, filed Aug. 30, 2004 and Ser. No.09/836,674, filed Apr. 16, 2001, the disclosures of which areincorporated herein by reference.

The growth processes can optionally be carried out in a reactor orreaction space connected to a cluster tool. In a cluster tool, becauseeach reaction space is dedicated to one type of process, the temperatureof the reaction space in each module can be kept constant, whichimproves the throughput compared to a reactor in which is the substrateis heated up to the process temperature before each run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

The following examples illustrate certain preferred embodiments of theinvention. They were carried out in an F120™ ALD reactor supplied by ASMMicrochemistry Oy, Espoo.

Te and Se Precursors for Atomic Layer Deposition

Any of the following precursors can be used in the various ALD processesdisclosed herein. In particular, precursors comprising Te and Se aredisclosed.

In some embodiments the Te or Se precursor has Te or Se bound to twosilicon atoms. For example it can have a general formula ofA(SiR¹R²R³)₂, wherein A is Te or Se and R¹, R², and R³ are alkyl groupscomprising one or more carbon atoms. The R¹, R², and R³ alkyl groups canbe selected independently of each other in each ligand based on thedesired physical properties of the precursor such as volatility, vaporpressure, toxicity, etc. In some embodiments, R¹, R² and/or R³ can behydrogen, alkenyl, alkynyl or aryl groups. In some embodiments, R¹, R²,R³ can be any organic groups containing heteroatoms, such as N, O, F,Si, P, S, Cl, Br or I. In some embodiments R¹, R², R³ can be halogenatoms. In some embodiments the Te precursor is Te(SiMe₂ ^(t)Bu)₂ and theSe precursor is Se(SiMe₂ ^(t)Bu)₂. In other embodiments the precursor isTe(SiEt₃)₂, Te(SiMe₃)₂, Se(SiEt₃)₂ or Se(SiMe₃)₂. In more preferredembodiments the precursor has a Te—Si or Se—Si bond and most preferablySi—Te—Si or Si—Se—Si bond structure.

In some embodiments the Te or Se precursor has a general formula of[R¹R²R³X¹]₃—Si-A-Si—[X²R⁴R⁵R⁶]₃, wherein A is Te or Se; and wherein R¹,R², R³, R⁴, R⁵ and R⁶, can be independently selected to be alkyl,hydrogen, alkenyl, alkynyl or aryl groups. In some embodiments, R¹, R²,R³, R⁴, R⁵ and R⁶ can be any organic groups containing also heteroatoms,such as N, O, F, Si, P, S, Cl, Br or I. In some embodiments R¹, R², R³,R⁴, R⁵ and R⁶ can be halogen atoms. In some embodiments X¹ and X² can beSi, N, or O. In some embodiments X¹ and X² are different elements. Inembodiments when X is Si then Si will be bound to three R groups, forexample [R¹R²R³Si]₃—Si-A-Si—[SiR⁴R⁵R⁶]₃. In embodiments when X is N thennitrogen will only be bound to two R groups ([R¹R²N]₃—Si-A-Si—[NR³R⁴]₃).In embodiments when X is O, the oxygen will only be bound to one Rgroup, for example [R¹—O]₃—Si-A-Si—[O—R²]₃. R¹, R², R³, R⁴, R⁵ and R⁶groups can be selected independently of each other in each ligand basedon the desired physical properties of the precursor such as volatility,vapor pressure, toxicity, etc

In some embodiments the Te or Se precursors is selected from the groupconsisting of: R¹R²R³Si—Si-A-Si—SiR⁴R⁵R⁶; R¹R²N—Si-A-Si—NR³R⁴;R¹—O—Si-A-Si—O—R²; or R¹R²Si-A-SiR³R⁴ with a double bond between siliconand one of the R groups. In other embodiments the Te or Se precursorcomprises: a ring or cyclical configuration comprising a Te or Se atomand multiple Si atoms; or comprises more than one Te atoms or more thanone Se atoms. In these embodiments A is Te or Se and R¹, R², R³, R⁴, R⁵and R⁶, are selected from the group consisting of alkyl, hydrogen,alkenyl, alkynyl, or aryl groups. In some embodiments the Te or Seprecursor is not A(SiR¹R²R³)₂.

In some embodiments the Te or Se precursor has a formula similar to theformulas described above, however the Si atom has a double bond to oneof the R groups in the ligand (e.g. A-Si═) wherein A is Te or Se. Forexample, a partial structure of the precursor formula is representedbelow:

In some embodiments the precursor contains multiple atoms of Si and Teor Se. For example, a partial structure of a precursor in one embodimentis represented below wherein A is Te or Se:

The Si atoms in the partial formula pictured above can also be bound toone or more R groups. In some embodiments, any of the R groups describedherein can be used.

In some embodiments the precursor contains a Si—Te—Si or Si—Se—Si bondstructure in a cyclical or ring structure. For example, a partialstructure of a precursor in one embodiment is represented below, whereinA is Te or Se.

The R group can comprise an alkyl, alkenyl, alkynyl, alkylsilyl,alkylamine or alkoxide group. In some embodiments the R group issubstituted or branched. In some embodiments the R group is notsubstituted and/or is not branched. The Si atoms in the partial formulapictured above can also be bound to one or more R groups. In someembodiments, any of the R groups described herein can be used.

Metal Precursors for ALD in Combination with Te or Se Precursors of thePresent Invention

Any of the following metal precursors can be used in the various ALDprocesses disclosed herein. Some metal precursors that can be used incombination with the Te and Se precursors disclosed herein. Inparticular metal precursors in which metal is bonded to nitrogen, oxygenor carbon and that have ability to form a bond with silicon arepreferred.

In some embodiments the metal precursor is metal-organic ororganometallic precursor. In some embodiments the metal precursor is ahalide precursor. In some embodiments the metal precursor has an adductforming ligand.

Preferred precursors include, but are not limited to metal halides,alkyls, alkoxides, amides, silylamides, amidinates, cyclopentadienyls,carboxylates, β-diketonates and β-diketoimines.

Preferred metals in metal precursors include, but are not limited to Sb,Ge, Bi, Zn, Cu, In, Ag, Au, Pb, Cd, Hg,

More preferred Sb precursors include, Sb halides, such as SbCl₃, SbBr₃and SbI₃, Sb alkoxides, such as Sb(OEt)₃ and Sb amides.

More preferred Ge precursors include Ge halides, such as GeCl₂ andGeBr₂, adducted derivatives of GeCl₂ and GeBr₂, such as GeCl₂-dioxane,

More preferred Bi precursors include Bi halides, such as BiCl₃.

More preferred Zn precursors include elemental Zn, Zn halides, such asZnCl₂, and alkyl zinc compounds such Zn(Et)₂ or Zn(Me)₂.

More preferred Cu compounds, include Cu carboxylates, such asCu(II)-pivalate, Cu halides, such as CuCl and CuCl₂, Cu β-diketonates,such as Cu(acac)₂ or Cu(thd)₂ and Cu-amidinates.

More preferred In compounds, include In halides, such as InCl₃ and Inalkyl compounds, such as In(CH₃)₃.

More preferred Pb compounds include Pb alkyls, such as tetraphenyl leadPh₄Pb or tetraethyl lead Et₄Pb.

Pulsing Order for Te and Se Compounds in ALD Cycles

The pulsing order for reactants in an ALD cycle can be chosen by theskilled artisan. Preferably the Te or Se compound precursor pulse isafter the metal precursor pulse and purge in the deposition cycle.However, different pulsing schemes for Te and Se compounds can be used.In some embodiments the Te or Se compound is pulsed as a secondprecursor. In some embodiments the Te or Se compound is pulsed as afirst precursor. A skilled artisan can determine the appropriate pulsingschemes for deposition of films comprising three or more elements, suchas Ge—Sb—Te.

Atomic Layer Deposition of Sb—Te

In some embodiments, Sb_(x)Te_(y), preferably Sb₂Te₃, films aredeposited by ALD preferably without the use of plasma; however in somecases plasma might be used, if needed. For example, if elemental Tefilms or Te-rich films are desired, plasma, such as hydrogen plasma,hydrogen radicals or atomic hydrogen, may be used. Another use forplasma is doping of the films, for example doping by O, N or Si may bedone using plasma. Reliable methods for forming Sb—Te thin films by ALDwithout hydrogen plasma are not previously known in the art. Findingsuitable Te and Sb precursors compatible with ALD processes has beenchallenging as many precursors do not result in film growth or areextremely toxic. Hydride reactants H₂Te and H₂Se are highly toxic gasesand thus are difficult to work with. Other reactants containinghydrogen-Te and hydrogen-Se bonds are also believed to be extremelytoxic. For example, it is know that the toxicity of arsenic basedcompounds increases as the number of hydrogen-As bonds increases. It islikely that the toxicity of Te and Se compounds also increases as thenumber of hydrogen-Te and hydrogen-Se bonds increases. The alkylderivatives R₂Te and R₂Se are less toxic and less volatile; however,they are not as reactive. Some of the compounds described herein mayhave some level of toxicity. However, it is preferable to use precursorswith lower toxicity with sufficient reactivity, when feasible.

FIG. 2 is a flow chart generally illustrating a method for forming aSb—Te thin film 20 in accordance with one embodiment. According to someembodiments, an Sb₂Te₃ thin film is formed on a substrate in a reactionchamber by an ALD type process comprising multiple Sb—Te depositioncycles, each deposition cycle comprising:

-   -   providing a first vapor phase reactant pulse comprising a Te        precursor 21 into the reaction chamber to form no more than        about a single molecular layer of the Te precursor on the        substrate;    -   removing excess first reactant from the reaction chamber 23;    -   providing a second vapor phase reactant pulse comprising an Sb        precursor 25 to the reaction chamber such that the Sb precursor        reacts with the Te precursor on the substrate to form Sb₂Te₃;        and    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber 27.

This can be referred to as the Sb—Te deposition cycle. Each Sb—Tedeposition cycle typically forms at most about one monolayer of Sb₂Te₃.The Sb—Te deposition cycle is repeated until a film of a desiredthickness is formed 29. In some embodiments an Sb—Te film of from about10 Å to about 2000 Å, preferably from about 50 Å to about 500 Å isformed.

Although the illustrated Sb—Te deposition cycle begins with provision ofthe Te precursor, in other embodiments the deposition cycle begins withthe provision of the Sb precursor.

In some embodiments, the reactants and reaction by-products can beremoved from the reaction chamber by stopping the flow of Te or Sbprecursor while continuing the flow of an inert carrier gas such asnitrogen or argon.

Preferably, the Te precursor has a formula of Te(SiR¹R²R³)₂, wherein R¹,R², and R³ are alkyl groups comprising one or more carbon atoms. The R¹,R², and R³ alkyl groups can be selected on the desired physicalproperties of the precursor such as volatility, vapor pressure,toxicity, etc. In some embodiments the Te precursor is Te(SiMe₂^(t)Bu)₂. In other embodiments the precursor is Te(SiEt₃)₂ orTe(SiMe₃)₂.

In some embodiments the Sb source is SbX₃, wherein X is a halogenelement. More preferably the Sb source is SbCl₃ or SbI₃.

In some embodiments the Te precursor is Te(SiEt₃)₂ and the Sb precursoris SbCl₃.

The substrate temperature during forming the Sb—Te thin film ispreferably less than 250° C. and more preferably less than 200° C. andeven more preferably below 100° C. If an amorphous thin film is desiredthe temperature can be lowered even further down to at or below about90° C. In some embodiments the deposition temperature can be below about80° C., below about 70° C., or even below about 60° C.

Pressure of the reactor can vary much depending from the reactor usedfor the depositions. Typically reactor pressures are below normalambient pressure.

The skilled artisan can determine the optimal reactant evaporationtemperatures based on the properties of the selected precursors. Theevaporation temperatures for the Te precursor, such as Te(SiMe₂ ^(t)Bu)₂and Te(SiEt₃)₂, which can be synthesized by the methods describedherein, is typically about 40° C. to 45° C. Te(SiMe₃)₂ has a slightlyhigher vapor pressure than Te(SiMe₂ ^(t)Bu)₂ or Te(SiEt₃)₂ and thusTe(SiMe₃)₂ evaporation temperature is slightly lower from about 20 to30° C. The evaporation temperature for the Sb precursor, such as SbCl₃,is typically about 30° C. to 35° C.

The skilled artisan can determine the optimal reactant pulse timesthrough routine experimentation based on the properties of the selectedprecursors and the desired properties of the deposited Sb—Te thin film.Preferably the Te and Sb reactants are pulsed for about 0.05 to 10seconds, more preferably about 0.2 to 4 seconds, and most preferablyabout 1 to 2 seconds. The purge steps in which excess reactant andreaction by-products, if any, are removed are preferably about 0.05 to10 seconds, more preferably about 0.2-4 seconds, and most preferably 1to 2 seconds in length.

The growth rate of the Sb—Te thin films will vary depending on thereaction conditions. As described below, in initial experiments, thegrowth rate varied between about 0.019 and 0.025 Å/cycle for higherreaction temperatures. Higher growth rates were observed at lowertemperatures. A maximum growth rate of about 0.65 Å/cycle was observedat lower temperatures, around 60° C.

In some embodiments, an Sb₂Te₃ thin film is deposited on a substrate andforms the active material in a PCM cell. The Sb₂Te₃ thin film preferablyhas a thickness of about 10 Å to about 2000 Å.

Example 1

Sb—Te thin films were formed using alternating and sequential pulses ofSbCl₃ and Te(SiMe₂ ^(t)Bu)₂. Pulse and purge lengths were 1 and 2seconds for SbCl₃ and 1 and 4 seconds for Te(SiMe₂ ^(t)Bu)₂. Sb—Te thinfilms were grown at approximately 100° C. on a silicon surface, sodalime glass, and rhodium. The Sb—Te thin films were deposited to athickness between about 9 nm and about 12 nm.

The morphology of each film was compared using FESEM (field emissionscanning electron microscope) images. In the FESEM images there werevisible isolated islands on the film formed on the silicon substrate.However, the films grown on soda lime glass and rhodium were continuous.

Example 2

Sb—Te films were deposited on silicon and on tungsten at approximately150° C. using Te(SiEt₃)₂ as the Te source and SbCl₃ as the Sb source.The SbCl₃ pulse length was about 1 second and the purge length was about2 seconds. The Te(SiEt₃)₂ pulse length was varied between about 0.2seconds and 2.0 seconds while the purge length was about 2 seconds. Thegrowth rate and composition were measured for the thin films formed withvarying Te precursor pulse lengths. The results are illustrated in FIGS.3-5, which also show error bars for each point estimating theuncertainty associated with the EDX measurement technique. As can beseen in FIG. 3, the growth rate per cycle ranged from about 0.019 to0.025 Å/cycle on silicon with native oxide and from about 0.023 to 0.073Å/cycle on tungsten depending on Te precursor pulse length. The exactcomposition of the films also varied with the pulse length of the Teprecursor on silicon with native oxide (FIG. 4) and tungsten (FIG. 5).

FIG. 6 is an x-ray diffractogram of a Sb—Te film grown on soda limeglass at 150° C. using a deposition cycle comprising:

a 1 second pulse of a SbCl₃;

a 2 second purge;

a 2 second pulse of Te(SiEt₃)₂; and

a 2 second purge.

The Sb₂Te₃ crystalline reflections (FIG. 6) indicate a high degree ofcrystallinity and strong (001)-orientation in the Sb₂Te₃ thin film.

Example 3

Sb—Te films were deposited on a substrate using Te(SiEt₃)₂ as the Tesource and SbCl₃ as the Sb source at varying temperatures and varyingprecursor pulse lengths. FIG. 19 is a graph of the composition of aSb—Te thin film deposited on a tungsten substrate at varying growthtemperatures. The Sb—Te thin films were deposited using 1 second pulsesof Te(SiEt₃)₂ and SbCl₃ reactants along with a 2 second purge betweeneach reactant pulse. The deposited Sb—Te film was close to thestoichiometric ratio of Sb₂Te₃ for temperatures of about 100° C. andbelow. Additionally, no chlorine impurities were detected by EDXanalysis. For higher temperatures, above about 120° C., the Sb—Te filmscontained slightly more antimony than the stoichiometric ratio ofSb₂Te₃.

FIG. 20 is a graph of the average growth rate per cycle of Sb—Te versusthe growth temperature for Sb—Te deposited on a tungsten substrate and asilicon substrate. The Sb—Te thin films were deposited using 1 secondpulses of Te(SiEt₃)₂ and SbCl₃ reactants along with a 2 second purgebetween each reactant pulse. The observed growth rate was higher atlower temperatures, with a maximum average growth rate of about 0.65Å/cycle at a temperature of about 70° C. The growth rate decreased tobelow 0.1 Å/cycle at substrate temperatures above about 120° C. Thegrowth rate on tungsten and silicon substrates exhibited similar trends,however, the growth rate observed on tungsten was slightly higher.

FIGS. 21 and 22 are graphs of the average growth rates per cycle for thedeposition of Sb—Te thin films on silicon substrates varying the Sb andTe pulse lengths, respectively. SbCl₃ and Te(SiEt₃)₂ were used as the Sband Te sources, respectively. The thin films were deposited at atemperature of 60° C. A pulse length of 1 second was used for thereactant that was not varied. The purge length between precursor pulseswas 2 seconds. Both graphs illustrate a saturating growth rate of about0.6 Å/cycle.

Example 4

Sb—Te films were deposited on silicon and on tungsten at approximately90° C. using Te(SiMe₃)₂ as the Te source and SbCl₃ as the Sb source. TheSbCl₃ pulse length was about 1 second and the purge length was about 2seconds. The Te(SiMe₃)₂ pulse length was about 2 seconds while the purgelength was about 2 seconds. SbCl₃ source temperature was about 30° C.and Te(SiMe₃)₂ was at room temperature, at about 22° C. After 2000cycles films were analyzed by EDX, which revealed that the films wereSb₂Te₃.

Atomic Layer Deposition of Sb—Se

In other embodiments a Sb_(x)Se_(y), preferably Sb₂Se₃, film can beformed essentially as described above, by using a Se precursor insteadof a Te precursor. The Se precursor preferably has a formula ofSe(SiR¹R²R³)₂, wherein R¹, R², and R³ are alkyl groups with one or morecarbon atoms. The skilled artisan can choose R¹, R², and R³ alkyl groupsbased on the desired physical properties of the precursor such asvolatility, vapor pressure, toxicity, etc. In some embodiments the Seprecursor is Se(SiMe₂ ^(t)Bu)₂. In other embodiments the Se precursor isSe(SiEt₃)₂. The ALD process conditions for forming a Sb—Se thin film,such as temperature, pulse/purge times, etc. can be as described abovefor the deposition of Sb—Te films.

ALD of Ge—Te

In other embodiments, a Ge_(x)Te_(y), preferably GeTe, thin film isformed by ALD without the use of plasma. FIG. 7 is a flow chartgenerally illustrating a method for forming a Ge—Te thin film 70 inaccordance with some embodiments. A Ge—Te thin film is formed on asubstrate by an ALD type process comprising multiple Ge—Te depositioncycles, each deposition cycle comprising:

-   -   providing a first vapor phase reactant pulse comprising a Te        precursor 71 into the reaction chamber to form no more than        about a single molecular layer of the Te precursor on the        substrate;    -   removing excess first reactant from the reaction chamber 73;    -   providing a second vapor phase reactant pulse comprising a Ge        precursor 75 to the reaction chamber such that the Ge precursor        reacts with the Te precursor on the substrate; and    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber 77.

This can be referred to as the Ge—Te deposition cycle. Each Ge—Tedeposition cycle typically forms at most about one monolayer of Ge—Te.The Ge—Te deposition cycle is repeated until a film of a desiredthickness is formed 79. In some embodiments a Ge—Te film of from about10 Å to about 2000 Å is formed.

Although the illustrated Ge—Te deposition cycle begins with provision ofthe Te precursor, in other embodiments the deposition cycle begins withthe provision of the Ge precursor.

In some embodiments, the reactants and reaction by-products can beremoved from the reaction chamber by stopping the flow of Te or Geprecursor while continuing the flow of an inert carrier gas such asnitrogen or argon.

Preferably, the Te precursor has a formula of Te(SiR¹R²R³)₂, wherein R¹,R², and R³ are preferably alkyl groups with one or more carbon atoms.The skilled artisan can choose R¹, R², and R³ alkyl groups based on thedesired physical properties of the precursor such as volatility, vaporpressure, toxicity, etc. In some embodiments the Te precursor isTe(SiMe₂ ^(t)Bu)₂. In other embodiments the Te precursor is Te(SiEt₃)₂or Te(SiMe₃)₂.

Preferably, the Ge source is GeX₂ or GeX₄, wherein X is a halogenelement. In some embodiments the Ge source is GeBr₂. In some embodimentsthe Ge source is germanium halide with coordinating ligands, such asdioxane ligands. Preferably the Ge source with coordinating ligands isgermanium dihalide complex, more preferably a germanium dichloridedioxane complex GeCl₂.C₄H₈O₂.

The substrate temperature during deposition of the Ge—Te thin film ispreferably less than about 300° C. and more preferably less than about200° C. and even more preferably less than about 150° C. When GeBr₂ isused as the Ge precursor the process temperature is typically aboveabout 130° C.

In some embodiments, however, the substrate temperature duringdeposition of the Ge—Te thin film is preferably less than 130° C. Forexample, when a germanium halide with coordinating ligands, such asGeCl₂—C₄H₈O₂ (germanium chloride dioxane) is used as the Ge precursorthe process temperature can be as low as about 90° C. The vaporizationtemperature of GeCl₂—C₄H₈O₂ is around 70° C., which can allow depositiontemperatures as low as about 90° C.

The skilled artisan can determine the reactant pulse times based on theproperties of the selected precursors, the other reaction conditions andthe desired properties of the deposited thin film. Preferably the Te andGe reactant pulses are from about 0.05 to 10 seconds, more preferablythe reactant pulses are from about 0.2 to 4 seconds, and most preferablythe reactant pulses are from about 1 to 2 seconds in length. The purgesteps are preferably about 0.05 to 10 seconds, more preferably about0.2-4 seconds, and most preferably about 1 to 2 seconds in length.

The growth rate of the Ge—Te thin film may vary depending on thereaction conditions, including the length of the precursor pulses. Asdiscussed below, in initial experiments a growth rate of around 0.15Å/cycle was observed on silicon with native oxide with substratetemperatures around 150° C.

Example 5

Ge—Te thin films were deposited on silicon with native oxide and glasssubstrates at approximately 150° C. using Te(SiEt₃)₂ as the Te sourceand GeBr₂ as the Ge source.

a 1 second GeBr₂ pulse;

a 2 second purge;

a 1 second Te(SiEt₃)₂ pulse; and

a 2 second purge.

The growth rate per cycle was calculated at about 0.15 Å/cycle. FIG. 8illustrates x-ray diffractogram results for a GeTe film on glass,indicating that the film was weakly crystalline. Energy dispersive x-ray(EDX) analysis showed that the films were slightly germanium rich atabout 56% to about 58% Ge and 42% to 44% tellurium.

Example 6

Ge—Te thin films were deposited on substrates at approximately 90° C.using Te(SiEt₃)₂ as the Te source and GeCl₂—C₄H₈O₂ as the Ge source.

a 1 second GeCl₂—C₄H₈O₂ pulse;

a 2 second purge;

a 1 second Te(SiEt₃)₂ pulse; and

a 2 second purge.

The growth rate per cycle was calculated at about 0.42 Å/cycle, which ishigher than the growth rate achieved with GeBr₂. X-ray diffractogramresults indicated that the thin film comprised rhombohedral GeTe alongwith a noticeable fraction of amorphous phase GeTe. Energy dispersivex-ray (EDX) analysis showed that the films were slightly germanium richat about 54% Ge and 46% tellurium.

Example 7

Ge—Te films were deposited on silicon and on tungsten at approximately90° C. using Te(SiMe₃)₂ as the Te source and GeCl₂—C₄H₈O₂ as the Gesource. The GeCl₂—C₄H₈O₂ pulse length was about 1 second and the purgelength was about 2 seconds. The Te(SiMe₃)₂ pulse length was about 2seconds while the purge length was about 2 seconds. GeCl₂—C₄H₈O₂ sourcetemperature was about 70° C. and Te(SiMe₃)₂ was at room temperature, atabout 22° C. After 1000 cycles, films were analyzed by EDX, whichrevealed that the films were GeTe.

ALD of GeSe

In other embodiments a Ge_(x)Se_(y), preferably GeSe film can be formedessentially as described above, but using a Se precursor instead of a Teprecursor. The Se precursor preferably has a formula of Se(SiR¹R²R³)₂,wherein R¹, R², and R³ are preferably alkyl groups with one or morecarbon atoms. The skilled artisan can choose R¹, R², and R³ alkyl groupsbased on the desired physical properties of the precursor such asvolatility, vapor pressure, toxicity, etc. In some embodiments the Seprecursor is Se(SiMe₂ ^(t)Bu)₂. In other embodiments the Se precursor isSe(SiEt₃)₂. The ALD process conditions for forming a GeSe thin film,such as temperature, pulse/purge times, etc. can be selected by theskilled artisan based on routine experimentation and are essentially asdescribed above for forming GeTe thin films.

ALD of Ge—Sb—Te

According to some embodiments, Ge_(x)Sb_(y)Te_(z), preferably Ge₂Sb₂Te₅,(GST) thin films are formed on a substrate by an ALD type processcomprising multiple deposition cycles. In particular, a number of Ge—Teand Sb—Te deposition cycles are provided to deposit a GST film with thedesired stoichiometry and the desired thickness. The Ge—Te and Sb—Tecycles can be as described above. The skilled artisan will appreciatethat multiple Sb—Te deposition cycles can be performed consecutivelyprior to a Ge—Te cycle, and that multiple Ge—Te deposition cycles can beperformed consecutively prior to a subsequent Sb—Te deposition cycle.The particular ratio of cycles can be selected to achieve the desiredcomposition. In some embodiments the GST deposition process begins witha Ge—Te deposition cycle and in other embodiments the GST depositionprocess begins with an Sb—Te deposition cycle. Similarly, the GSTdeposition process may end with a Ge—Te deposition cycle or a Sb—Tedeposition cycle.

In some preferred embodiments, the Sb—Te and Ge—Te cycles are providedin a 1:1 ratio, meaning they are alternately performed. In otherembodiments, the ratio of Sb—Te cycles to the total number of cycles(Ge—Te and Sb—Te cycles combined) is selected such that the compositionsof Ge and Sb in the deposited GST thin film are approximately the same.In some embodiments the ratio of Sb—Te cycles to Ge—Te cycles can bebetween about 100:1 and 1:100.

FIG. 9 is a flow chart generally illustrating a method for forming aGe—Sb—Te (GST) thin film 90 in accordance with one such embodiment. Asillustrated in FIG. 9 the method comprises:

-   -   providing a first vapor phase reactant pulse comprising a Te        precursor 91 into the reaction chamber to form no more than        about a single molecular layer of the Te precursor on the        substrate;    -   removing excess first reactant from the reaction chamber 92;    -   providing a second vapor phase reactant pulse comprising an Sb        precursor 93 to the reaction chamber such that the Sb precursor        reacts with the Te precursor on the substrate;    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber 94;    -   providing a third vapor phase reactant pulse comprising a Te        precursor 95 into the reaction chamber to form no more than        about a single molecular layer of the Te precursor on the        substrate;    -   removing excess third reactant from the reaction chamber 96;    -   providing a fourth vapor phase reactant pulse comprising a Ge        precursor 97 to the reaction chamber such that the Ge precursor        reacts with the Te precursor on the substrate;    -   removing excess fourth reactant and reaction byproducts, if any,        from the reaction chamber 98.

The providing and removing steps are repeated until a film of a desiredthickness is formed 99.

The process conditions, precursors, and pulse/purge times aresubstantially similar to those discussed above.

In some embodiments the GST thin film can be crystalline as deposited.In other embodiments an amorphous GST thin film is deposited. In someembodiments, the amorphous thin film can be annealed in the presence ofan inert gas, such as nitrogen. The substrate and thin film can also beheated during the annealing step at a temperature above the depositiontemperature. Preferably, the substrate temperature during the annealingstep is above about 130° C. More preferably, the substrate temperatureduring the annealing step is above about 250° C. Most preferably thetemperature during the annealing step is above 300° C. The annealingstep can change the crystallinity of the thin film. In some embodimentsan amorphous thin film can crystallize during the annealing step. Insome embodiments the crystallinity of a crystalline GST thin film canchange during the annealing step.

Example 8

A Ge—Sb—Te thin film was formed on a substrate by alternating ALD cyclesof Sb—Te and Ge—Te. The ratio of Sb—Te:Ge—Te ALD cycles was 1:1. Thesubstrate temperature was about 150° C. The reactants and pulse andpurge lengths were as follows:

SbCl₃ 1 second; Purge 2 seconds; Te(SiEt₃)₂ 1 second; Purge 2 seconds;GeBr₂ 0.2 to 2 seconds (varied) Purge 2 seconds; Te(SiEt₃)₂ 1 second;and Purge 2 seconds.

Results from these experiments are shown in FIGS. 10-13. FIG. 10illustrates the average deposition thickness per cycle calculated bydividing the overall film thickness by the number of Te(SiEt₃)₂ pulses.The film thickness deposited per cycle varied between 0.05 and 0.15Å/cycle. FIG. 11 illustrates the atomic composition of the depositedGe—Sb—Te thin films. The Ge—Sb—Te composition is close to stoichiometricfor GeBr₂ pulse lengths between 0.6 and 2.0 seconds. These resultsindicate that Sb—Te deposition is more efficient on Ge—Te than on Sb—Tealone as the film growth rate was around 0.025 Å/cycle for Sb—Te alone.

The morphology and crystal structure of the Ge—Sb—Te thin films alsovaried depending on the GeBr₂ pulse lengths. FIG. 12 shows an x-raydiffractogram for Ge—Sb—Te thin films formed with 0.2 s, 1.0 s, and 1.5s pulses of GeBr₂. The film formed with 0.2 second pulses of GeBr₂ showsa crystalline structure with peaks corresponding to the Sb₂Te₃crystalline structures. As the pulse length of GeBr₂ increases the filmdeveloped a crystalline structure closer to Ge—Sb—Te. FIG. 13 shows agracing incidence x-ray diffractogram for a film formed with 1 secondpulses of GeBr₂. The film exhibits Ge₂Sb₂Te₅ crystalline reflections.

The growth rate per cycle was also studied for various GeBr₂ sourcetemperatures. The process conditions were as described above in thisexample, with a GeBr₂ pulse length of 1 second, FIG. 24 illustrates thegrowth rate per cycle versus GeBr₂ source temperatures between 90° C.and 125° C. The growth rate per cycle increases as temperatureincreases.

The composition of the Ge—Sb—Te thin film across the substrate was alsostudied. FIG. 23 is a graph of the composition of the Ge—Sb—Te thin filmat various places on the substrate. The flat lines indicate that thecomposition of the Ge—Sb—Te thin film is consistent across thesubstrate. FIG. 25 is a graph of the average growth rate per cycle atdifferent locations on the substrate for substrate depositiontemperatures of 90° C., 100° C., and 120° C. The average growth rate percycle increased with increasing temperature and varied slightly acrossthe substrate.

Example 9

A Ge—Sb—Te thin film was formed on a substrate by alternating ALD cyclesof Sb—Te and Ge—Te. The ratio of Sb—Te:Ge—Te ALD cycles was 1:1. Thephysical properties of GeCl₂—C₄H₈O₂ allowed for lower depositiontemperatures. The reactants and pulse and purge lengths were as follows:

SbCl₃ 1 second; Purge 2 seconds; Te(SiEt₃)₂ 1 second; Purge 2 seconds;GeCl₂—C₄H₈O₂ 1-6 seconds (varied) Purge 2 seconds; Te(SiEt₃)₂ 1 second;and Purge 2 seconds.

Results from these experiments are shown in FIGS. 26-28.

FIG. 26 is a FESEM image of a GST thin films deposited in high aspecttrench structures. The deposition conditions were essentially asdescribed above in the Examples, however, a Ge—Te/(Ge—Te+Sb₂Te₃) cyclingratio of 0.33 was used. The FESEM image shows that the film thickness inthe trench structure of about 65 nm is virtually the same in differentparts of the structure. The image shows that the ALD process using theseprecursors is capable of depositing uniform and highly conformal thinfilms in high aspect ratio structures, such as trench structures.

FIG. 27 is a gracing incidence X-ray diffractogram of a GST thin filmwith a composition of 23% Ge, 28% Sb, and 49% Te that was subjected tohigh temperature XRD measurements. The GST thin film was annealed in thepresence of a nitrogen flow with XRD measurements done in situ. The GSTthin film was amorphous as deposited at a temperature of about 90° C.The GST thin film began to crystallize at 130° C. exhibiting reflectionsbelonging to the meta-stable rock salt structure. As the annealingtemperature increased gradually, the crystalline structure changed tothe stable hexagonal phase. The cubic and hexagonal phases are clearlydistinguished in FIG. 27.

FIG. 28A illustrates the composition of a GST thin film deposited withvarying pulse lengths of GeCl₂-dioxane. FIG. 28A shows that increasingthe pulse length of GeCl₂-dioxane increases the amount of Ge anddecreases the amount of Te in the GST thin film when GeCl₂-dioxane pulselength is less than about 4 seconds in the used reactor. FIG. 28A alsoshows that film composition saturates when GeCl₂-dioxane pulse length ismore than about 4 seconds in the used reactor. Saturation may happenwith different GeCl₂-dioxane pulse lengths at different reactors. FIG.28B is a graph of the composition of various GST thin films for variousGe—Te/(Ge—Te+Sb—Te) cycling ratios. FIG. 28B shows that a cycling ratioof about 0.35 should result in a GST thin film with about equalcompositions of Ge and Sb.

Example 10

Sb—Te and Ge—Sb—Te films were deposited on 200 mm silicon substrates ina Pulsar® 2000 reactor by using SbCl₃, Te(SiEt₃)₂ and GeCl₂.dioxane as aprecursors at growth temperatures of 70° C. and 90° C. Precursortemperatures for SbCl₃, Te(SiEt₃)₂ and GeCl₂.dioxane were 45° C., 60° C.and 60° C., respectively. Precursor pulse times for SbCl₃, Te(SiEt₃)₂and GeCl₂.dioxane were about 0.5 seconds, 0.5 seconds and from about 5to about 15 seconds, respectively. Precursor purge times for SbCl₃,Te(SiEt₃)₂ and GeCl₂.dioxane were varied in the range of 1 seconds to 20seconds. Films had full coverage with relatively good uniformity acrossthe 200 mm wafer, EDX revealed the films to be nearly stoichiometricSb₂Te₃ and Ge₂Sb₂Te₅.

ALD of Ge—Sb—Se

In other embodiments a Ge_(x)Sb_(y)Se_(z), preferably GeSbSe film, canbe formed by using a Se precursor instead of a Te precursor in theprocess described above for Ge—Sb—Te. The Se precursor preferably has aformula of Se(SiR¹R²R³)₂, wherein R¹, R², and R³ are preferably alkylgroups with one or more carbon atoms. The skilled artisan can choose R¹,R², and R³ alkyl groups based on the desired physical properties of theprecursor such as volatility, vapor pressure, toxicity, etc. In someembodiments the Se precursor is Se(SiMe₂ ^(t)Bu)₂ and in otherembodiments is Se(SiEt₃)₂. The ALD process conditions for forming aGe—Sb—Se thin film are essentially as described above for forming a GSTfilm, with an Sb—Se deposition cycle substituted for the Sb—Tedeposition cycles and a Ge—Se deposition cycle substituted for the Ge—Tedeposition cycles.

ALD of Bi—Te

FIG. 14 is a flow chart generally illustrating methods for forming Bi—Tethin films 140 in accordance with some embodiments. A Bi_(x)Te_(y),preferably BiTe, thin film is formed on a substrate by an ALD typeprocess comprising multiple Bi—Te deposition cycles, each Bi—Tedeposition cycle comprising:

-   -   providing a first vapor phase reactant pulse comprising a Te        precursor 141 into the reaction chamber to form no more than        about a single molecular layer of the Te precursor on the        substrate;    -   removing excess first reactant from the reaction chamber 143;    -   providing a second vapor phase reactant pulse comprising a Bi        precursor 145 to the reaction chamber such that the Bi precursor        reacts with the Te precursor on the substrate; and    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber 147.

Each Bi—Te deposition cycle typically forms at most about one monolayerof Bi—Te. The Bi—Te deposition cycle is repeated until a film of adesired thickness is formed 149. In some embodiments a Bi—Te film offrom about 10 Å to about 2000 Å is formed.

Although the illustrated Bi—Te deposition cycle begins with provision ofthe Te precursor, in other embodiments the deposition cycle begins withthe provision of the Bi precursor.

In some embodiments, the reactants and reaction by-products can beremoved from the reaction chamber by stopping the flow of Te or Biprecursor while continuing the flow of an inert carrier gas such asnitrogen or argon.

Preferably, the Te precursor has a formula of Te(SiR¹R²R³)₂, wherein R¹,R², and R³ are alkyl groups comprising one or more carbon atoms. The R¹,R², and R³ alkyl groups can be selected based on the desired physicalproperties of the precursor such as volatility, vapor pressure,toxicity, etc. In some embodiments the Te precursor is Te(SiMe₂^(t)Bu)₂. In other embodiments the precursor is Te(SiEt₃)₂.

Preferably, the Bi precursor has a formula of BiX₃, wherein X is ahalogen element. In some embodiments the Bi precursor is BiCl₃.

The process temperature during the Bi—Te deposition cycle is preferablyless than 300° C., and more preferably less than 200° C. The pulse andpurge times are typically less than 5 seconds, and preferably around 1-2seconds. The skilled artisan can choose pulse/purge times based on theparticular circumstances.

Example 11

A Bi₂Te₃ film was deposited on silicon and glass substrates at atemperature of about 175° C. using BiCl₃ and Te(SiEt₃)₂ precursors. Thepulse and purge times of the precursors were 1 and 2 seconds,respectively. The average growth rate per cycle was about 1.2 Å/cycle.Analysis of the film showed that the film composition was close to thestoichiometric ratio for Bi₂Te₃. FIG. 15 is a gracing incidence x-raydiffractogram of the Bi₂Te₃ film, which showed that the film wascrystalline and that the peaks corresponding to Bi₂Te₃ were pronounced.

ALD of Bi—Se

In other embodiments, a Bi_(x)Se_(y), preferably BiSe film is formed byusing a Se precursor instead of a Te precursor in the ALD processdescribed above for Bi—Te. The Se precursor preferably has a formula ofSe(SiR¹R²R³)₂, wherein R¹, R², and R³ are preferably alkyl groups withone or more carbon atoms. The skilled artisan can choose R¹, R², and R³alkyl groups based on the desired physical properties of the precursorsuch as volatility, vapor pressure, toxicity, etc. In some embodimentsthe Se precursor is Se(SiMe₂ ^(t)Bu)₂ and in other embodiments the Seprecursor is Se(SiEt₃)₂. The ALD process conditions for forming a Bi—Sethin film, such as temperature, pulse/purge times, etc. can be selectedby the skilled artisan and are essentially as described above for Bi—Te.

ALD of Zn—Te

FIG. 16 is a flow chart generally illustrating methods for forming Zn—Tethin films 160. A Zn_(x)Te_(y), preferably ZnTe, thin film can be formedon a substrate by an ALD type process comprising multiple Zn—Tedeposition cycles, each Zn—Te deposition cycle comprising:

-   -   providing a first vapor phase reactant pulse comprising a Te        precursor 161 into the reaction chamber to form no more than        about a single molecular layer of the Te precursor on the        substrate;    -   removing excess first reactant from the reaction chamber 163;    -   providing a second vapor phase reactant pulse comprising a Zn        precursor 165 to the reaction chamber such that the Zn precursor        reacts with the Te precursor on the substrate; and    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber 167.

The Zn—Te cycle is repeated until a film of a desired thickness isformed 169. In some embodiments a Zn—Te film of from about 10 Å to about2000 Å is formed.

Although the illustrated Zn—Te deposition cycle begins with provision ofthe Te precursor, in other embodiments the deposition cycle begins withthe provision of the Zn precursor.

In some embodiments, the reactants and reaction by-products can beremoved from the reaction chamber by stopping the flow of Te or Znprecursor while continuing the flow of an inert carrier gas such asnitrogen or argon.

Preferably, the Te precursor has a formula of Te(SiR¹R²R³)₂, wherein R¹,R², and R³ are preferably alkyl groups with one or more carbon atoms.The skilled artisan can choose R¹, R², and R³ alkyl groups based on thedesired physical properties of the precursor such as volatility, vaporpressure, toxicity, etc. In some embodiments the Te precursor isTe(SiMe₂ ^(t)Bu)₂. In other embodiments the Te precursor is Te(SiEt₃)₂.

Preferably, the Zn precursor has a formula of ZnX₂, wherein X is ahalogen element or an alkyl group. In some embodiments the Zn precursoris ZnCl₂ or Zn(C₂H₅)₂.

The process temperature during the Zn—Te deposition cycle is preferablyless than 500° C., and more preferably about 400° C. The pulse and purgetimes are typically less than 5 seconds, preferably about 0.2-2 seconds,and more preferably about 0.2-1 seconds. The skilled artisan can chooseappropriate pulse/purge times based on the particular circumstances.

Example 12

A Zn—Te film was deposited on a silicon with native oxide and a glasssubstrate at a deposition temperature of about 400° C., usingalternating and sequential pulses of ZnCl₂ and Te(SiEt₃)₂. Pulse andpurge lengths of 0.4 and 0.5 seconds, respectively, were used for bothprecursors.

The average growth rate per cycle was about 0.6 Å/cycle, EDX analysis ofthe film showed that the film was close to stoichiometric with acomposition of 47% Zn and 53% Te. FIG. 17 is an x-ray diffractogram ofthe Zn—Te thin film that was formed, illustrating that the film wascrystalline with a cubic configuration.

ALD of Zn—Se

In other embodiments a Zn_(x)Se_(y), preferably ZnSe, film can be formedby using a Se precursor in place of a Te precursor in the depositioncycle outlined above. The Se precursor preferably has a formula ofSe(SiR¹R²R³)₂, wherein R¹, R², and R³ are preferably alkyl groups withone or more carbon atoms. The skilled artisan can choose R¹, R², and R³alkyl groups based on the desired physical properties of the precursorsuch as volatility, vapor pressure, toxicity, etc. In some embodimentsthe Se precursor is Se(SiMe₂ ^(t)Bu)₂ and in other embodiments isSe(SiEt₃)₂. The ALD process conditions for forming a Zn—Se thin film,such as temperature, pulse/purge times, etc. can be selected by theskilled artisan and are essentially as described above for deposition ofZn—Te.

Example 13

Cu—In—Se films were deposited on both a silicon substrate with nativeoxide and a glass substrate at a deposition temperature of about 340° C.using alternating and sequential pulses of reactants. The reactants wereCuCl, InCl₃, and Se(SiEt₃)₂ and were at source temperatures of 325° C.,275° C. and 35° C., respectively. A Cu—Se cycle comprised alternatingand sequential pulses of CuCl and Se(SiEt₃)₂. An In—Se cycle comprisedalternating and sequential pulses of InCl₃ and Se(SiEt₃)₂. A pulsingratio of (Cu—Se) cycles to (In—Se) cycles was 1:1. Pulse and purgelengths of 1 and 2 seconds, respectively, were used for all precursors.FIG. 29 shows an EDX analysis of the deposited Cu—In—Se film. EDXanalysis revealed that the deposited film consisted of Cu, In and Se.

ALD of Compounds Comprising Selenide and Tellurium

Table 1 illustrates various thin films comprising tellurium or seleniumthat were deposited on glass and silicon substrates under variousprocess conditions. The thin films in Table 1 were deposited usingTe(SiEt₃)₂ as the tellurium source or Se(SiEt₃)₂ as the selenium source.

TABLE 1 Metal Growth precursor/ rate by evaporation Growth EDXComposition by Material temperature temperature (Å/cycle) EDX XRD ZnTeZnCl₂/360° C. 400° C. 0.6 Zn 47.0%, Te 53.0% ZnTe Bi₂Te₃ BiCl₃/140° C.165° C. 1.2 Bi 39.7%, Te 60.3% Bi₂Te₃ ZnSe ZnCl₂/360° C. 400° C. 0.55 Zn47.8%, Se 49.6%, Te 2.6%¹ ZnSe Bi₂Se₃ BiCl₃/140° C. 165° C. 0.97 Bi41.1%, Se 58.9% Bi₂Se₃ In₂Se₃ InCl₃/285° C. 295° C. 0.55 In 40.6%, Se59.4% In₂Se₃ CuSe Cu(II)-pivalate/ 165° C. 0.63 Cu 50.1%, Se 49.9% CuSe155° C. Cu_(2−x)Se Cu(II)-pivalate/ 200° C. 0.48 Cu 61.5%, Se 38.5%Cu_(2−x)Se 165° C. Cu₂Se Cu(II)-pivalate/ 300° C. 0.16 Cu 69.2%, Se30.8% Cu₂Se 165° C. Cu₂Se CuCl/350° C. 400° C. —² —² Cu₂Se ¹Tecontamination from previous runs ²no measurement

As shown in Table 1, the growth temperatures were higher for depositingsome films because the metal precursors had higher evaporationtemperatures. The results confirm that Te(SiEt₃)₂ and Se(SiEt₃)₂precursors can be used at higher temperatures, for example atapproximately 300° C.-400° C. In general, the thin films formed in Table1 exhibited good growth rates. Further, the compositions for most of thethin films were close to the theoretical stoichiometric ratio.

In general, the deposited thin films appeared to be of good quality withlittle visible variation across the thin film surface.

The deposited copper-selenium (Cu—Se) thin films illustrated interestingresults with Cu(II)-pivalate as the copper precursor. The stoichiometryof the deposited thin film varied with the growth temperature. CuSe wasdeposited at growth temperature of 165° C. Cu_(2-x)Se was deposited at agrowth temperature of 200° C. Cu₂Se was deposited at a growthtemperature of 300° C.

In some embodiments, any of the thin films described above can be dopedwith desired dopants for phase change memory applications, such as N, O,Si, S, In, Ag, Sn, Au, As, Bi, Zn, Se, Te, Ge, Sb and Mn, by addingpulses of a corresponding precursor to the growth process.

For example, for solar cells absorber materials like CuInSe₂ some of theIn can be replaced, for example, by Ga and some of the Se can bereplaced by, for example S, to modify the properties of the film toachieve the desired properties.

In some embodiments solar cell absorber materials can comprise Te. Insome embodiments solar cell absorber materials can comprise Se.

In some embodiments Cu—Se thin films can be used as solar cell absorbermaterials. In other embodiments Cu—Se thin films can be modified to formsolar cell absorber materials, for example, by doping as described aboveor other modification of the properties of the Cu—Se thin films. In someembodiments Cu—In—Se thin films can be used as solar cell absorbermaterials. In some embodiments, Cu—In—Se thin films doped to replacesome or all of the In or Se atoms are used as solar cell absorbermaterials.

In some embodiments, any of the thin films described above can bedeposited on any kind of substrate or surface such as, silicon, siliconoxide, silicon with native oxide, glass, semiconductor, metal oxide, andmetal. In some cases, a metal surface, such as a tungsten surface, ispreferred because of the higher growth rate as shown in FIG. 3. Othersuitable metal surfaces include, but are not limited to, TiN, TaN_(x),Ti, Ta, Nb, NbN_(x), MoN_(x), Mo, WN_(x), Cu, Co, Ni, Fe, Al and noblemetals.

Te(SiR¹R²R³)₂ or Se(SiR¹R²R³)₂ have suitable vapor pressures atrelatively low temperatures and relatively high decompositiontemperatures, which are required for ALD processes. Thus thoseprecursors can be used for ALD of other films than those described inthis application.

Precursor Synthesis

Methods are also provided for making some of the precursors used in theALD processes described herein. In some embodiments, the precursorcomprising Te or Se has a Te or Se atom bound to two silicon atoms. Inparticular, Te and Se precursors having a formula of Te(SiR¹R²R³)₂ orSe(SiR¹R²R³)₂, wherein R¹, R², and R³ are preferably alkyl groups withone or more carbon atoms, can be synthesized. In some embodiments the Teprecursor that is synthesized is Te(SiMe₂ ^(t)Bu)₂ and in otherembodiments is Te(SiEt₃)₂. The Se precursor that is synthesized isSe(SiMe₂ ^(t)Bu)₂ in some embodiments and Se(SiEt₃)₂ in otherembodiments.

In some embodiments the Te or Se precursor that is synthesized has ageneral formula of A(SiR¹R²R³)₂, wherein A is Te or Se and R¹, R², andR³ are alkyl groups comprising one or more carbon atoms. The R¹, R², andR³ alkyl groups can be selected independently of each other in eachligand based on the desired physical properties of the precursor such asvolatility, vapor pressure, toxicity, etc. In some embodiments, R¹, R²and/or R³ can be hydrogen, alkenyl, alkynyl or aryl groups. In someembodiments R¹, R², R³ can be any organic groups containing heteroatoms,such as N, O, F, Si, P, S, Cl, Br or I. In some embodiments R¹, R², R³can be halogen atoms. In some embodiments the Te precursor is Te(SiMe₂^(t)Bu)₂ and the Se precursor is Se(SiMe₂ ^(t)Bu)₂. In other embodimentsthe precursor is Te(SiEt₃)₂, Te(SiMe₃)₂, Se(SiEt₃)₂ or Se(SiMe₃)₂. Inmore preferred embodiments the precursor has a Te—Si or Se—Si bond andmost preferably Si—Te—Si or Si—Se—Si bond structure.

In some embodiments the Te or Se precursor that is synthesized has a Teor Se atom bound to two silicon atoms. For example, the precursor mayhave a general formula of [R¹R²R³X¹]₃—Si-A-Si—[X²R⁴R⁵R⁶]₃, wherein A isTe or Se; and wherein R¹, R², R³, R⁴, R⁵ and R⁶, can be independentlyselected to be alkyl, hydrogen, alkenyl, alkynyl or aryl groups. In someembodiments R¹, R², R³, R⁴, R⁵ and R⁶ can be any organic groupcontaining heteroatoms, such as N, O, F, Si, P, S, Cl, Br or I. In someembodiments R¹, R², R³, R⁴, R⁵ and R⁶ can be halogen atoms. In someembodiments X¹ and X² can be Si, N, or O. In some embodiments X¹ and X²are different elements. In embodiments when X is Si then Si will bebound to three R groups, for example [R¹R²R³Si]₃—Si-A-Si—[SiR⁴R⁵R⁶]₃. Inembodiments when X is N then nitrogen will only be bound to two R groups([R¹R²N]₃—Si-A-Si—[NR³R⁴]₃). In embodiments when X is O, then oxygenwill only be bound to one R group, for example [R¹—O]₃—Si-A-Si—[O—R²]₃.R¹, R², R³, R⁴, R⁵ and R⁶ groups can be selected independently of eachother in each ligand based on the desired physical properties of theprecursor such as volatility, vapor pressure, toxicity, etc

In some embodiments the Te or Se precursor that is synthesized has aformula similar to the formulas described above, however the Si atom hasa double bond to one of the R groups in the ligand (e.g. A-Si═) whereinA is Te or Se. For example, a partial structure of the precursor formulais represented below:

In some embodiments the precursor that is synthesized contains multipleatoms of Si and Te or Se. For example, a partial structure of aprecursor in one embodiment is represented below wherein A is Te or Se:

The Si atoms in the partial formula pictured above can also be bound toone or more R groups. In some embodiments, any of the R groups describedherein can be used.

In some embodiments the precursor that is synthesized contains aSi—Te—Si or Si—Se—Si bond structure in a cyclical or ring structure. Forexample, a partial structure of a precursor in one embodiment isrepresented below, wherein A is Te or Se.

R group can comprise an alkyl, alkenyl, alkynyl, alkylsilyl, alkylamineor alkoxide group. In some embodiments the R group is substituted orbranched. In some embodiments the R group is not substituted and/or isnot branched. The Si atoms in the partial formula pictured above canalso be bound to one or more R groups. In some embodiments, any of the Rgroups described herein can be used.

FIG. 18 is a flowchart generally illustrating methods for forming Te orSe precursors 180. In some embodiments the process for making a Te or Seprecursor comprises:

-   -   forming a first product by reacting a Group IA metal with a        material comprising Te or Se 181; and    -   subsequently adding a second reactant comprising R¹R²R³SiX to        the first product, wherein R¹, R² and R³ are alkyl groups with        one or more carbon atoms and X is a halogen atom 183, thereby        forming A(SiR¹R²R³)₂, wherein A is Te or Se 185.

In some embodiments, a Group IA elemental metal, such as Li, Na, K, etc.is combined with elemental Te or Se. In some embodiments the materialcomprising Te or Se is elemental Te or Se. Preferably, the Group IAelement is provided as a powder or flakes and the elemental Te or Se isprovided as a metal powder.

In some embodiments, a solvent, such as tetrahydrofuran (THF, (CH₂)₄O),is added to the Group IA metal and Te or Se. Preferably, naphthalene(C₁₀H₈) is added to the mixture to facilitate the solubility of IA metaland therefore also to help reduce Te or Se.

In some embodiments, the mixture is heated and a reflux condenser isused to reflux the solution under an inert gas such as Argon untilcompletion of the reaction. During the reflux period, the color of thesolution changes from clear and colorless to violet (with lithium as thereactant, other Group IA elements produce different colors) and then toa clear solution with a white precipitate. After a desired intermediateproduct is formed, the solution can be cooled down.

In some embodiments, a silicon containing compound is then added to themixture. Preferably the silicon containing compound comprises a siliconatom bound to a halogen atom. Preferably, the silicon containingcompound has a formula of R¹R²R³SiX, wherein R¹, R², and R³ arepreferably alkyl groups with one or more carbon atoms and X ispreferably a halogen atom. R¹, R², and R³ can be chosen based on thedesired precursor properties of the final product, including vaporpressure, melting point, etc. In some embodiments, R¹, R² and/or R³ canbe hydrogen, alkenyl, alkynyl or aryl groups. In some embodiments, R¹,R², R³ can be any organic group containing heteroatoms, such as N, O, F,Si, P, S, Cl, Br or I. In some embodiments R¹, R², R³ can be halogenatoms. In some embodiments R¹, R², and R³ can all be the same group. Inother embodiments, R¹, R², and R³ can all be different groups. In someembodiments, R¹, R², and R³ are all ethyl groups (Et₃). In otherembodiments R¹ and R² are methyl groups and R³ is a tertbutyl group (Me₂^(t)Bu). In some embodiments, X is Cl. In some preferred embodiments,the silicon containing compound has a formula of Et₃SiCl or^(t)BuMe₂SiCl.

In some embodiments the silicon containing compound has a generalformula of [R¹R²R³X¹]₃—Si—X, wherein R¹, R² and R³, can be independentlyselected to be alkyl, hydrogen, alkenyl, alkynyl or aryl groups and X ispreferably a halogen atom. In some embodiments R¹, R² and R³ can be anyorganic group containing heteroatoms, such as N, O, F, Si, P, S, Cl, Bror I. In some embodiments R¹, R² and R³ can be halogen atoms. In someembodiments X¹ can be Si, N, or O. In embodiments when X¹ is Si then Siwill be bound to three R groups, for example [R¹R²R³Si]₃—Si—X. Inembodiments when X¹ is N then nitrogen will only be bound to two Rgroups ([R¹R²N]₃—Si—X. In embodiments when X¹ is O, then oxygen willonly be bound to one R group, for example [R¹—O]₃—Si—X. R¹, R² and R³groups can be selected independently of each other in each ligand basedon the desired physical properties of the precursor such as volatility,vapor pressure, toxicity, etc

In some embodiments the silicon containing compound has a formulasimilar to the formulas described above, however the Si atom has adouble bond to one of the R groups in the ligand (e.g. bond structureX—Si═R) wherein R can be independently selected to be alkyl, hydrogen,alkenyl, alkynyl or aryl groups and X is preferably a halogen atom. Insome embodiments, R can be any organic group containing heteroatoms suchas N, O, F, Si, P, S, Cl, Br or I. For example, a partial structure ofthe silicon containing compound formula is represented below:

In some embodiments the silicon containing compound has a formulasimilar to the formulas described above, however the Si atom has two Xatoms attached to silicon (e.g. bond structure X₂—Si—R¹R²) wherein R¹and R² can be independently selected to be alkyl, hydrogen, alkenyl,alkynyl or aryl groups and X is preferably a halogen atom. In someembodiments R¹ and R² can be any organic group containing heteroatomssuch as N, O, F, Si, P, S, Cl, Br or I. For example, a partial structureof the silicon containing compound formula is represented below:

In some embodiments the silicon containing compound has a formulasimilar to the formulas described above, however there are two Si atomsbridged via R group (e.g. bond structure X—Si—R—Si—X) wherein R groupcan comprise an alkyl, alkenyl, alkynyl, alkylsilyl, alkylamine oralkoxide group. In some embodiments the R group is substituted orbranched. In some embodiments the R group is not substituted and/or isnot branched and X is preferably a halogen atom. In some embodiments, Rcan be any organic group containing heteroatoms such as N, O, F, Si, P,S, Cl, Br or I.

In some embodiments the silicon containing compound is selected from thegroup consisting of: R¹R²R³Si—Si—X, R¹R²N—Si—X, R¹—O—Si—X, R¹R²Si—X witha double bond between silicon and one of the R groups, or comprisesR¹R²—Si—X₂; wherein R¹, R², and R³, are selected from the groupconsisting of alkyl, hydrogen, alkenyl, alkynyl, or aryl groups and X isa halogen atom. In some embodiments the silicon containing compound isnot a compound of the formula XSiR¹R²R³.

The mixture is continuously stirred until the reaction is complete.After the reaction is substantially complete, the final product isseparated and isolated from any solvents, by-products, excess reactants,or any other compounds that are not desired in the final product. Theproduct can be a solid or liquid at standard temperature and pressure.

The following are examples of synthesizing Te compounds, but similarsynthesis methods can be used to synthesize corresponding Se compounds.

Example 14

Te(SiMe₂ ^(t)Bu)₂ was produced by the following process. First, 1.15 gof lithium (165.68 mmol) was added to 300 ml of dry THF along with 10.58g (89.22 mmol) of Te powder and 0.7 g (5.47 mmol) of naphthalene in a600 ml Schlenk bottle. The resultant mixture was heated and a refluxcondenser was mounted on the bottle. The solution was refluxed with anargon atmosphere for about four hours. The solution was initiallycolorless with undissolved solid Li and Te. During, the reflux periodthe mixture turned a violet color and then back to a clear solution witha white precipitate. After the white precipitate was formed, thesolution was cooled to 0° C.

Next, 25.00 g of ^(t)BuMe₂SiCl (165.87 mmol) was added to the mixture.The mixture was constantly stirred at room temperature over night. Themixture was then evaporated to dryness. 100 ml of toluene was added tothe dry mixture to facilitate filtering of the mixture. The toluenesolution was then filtered. The filtrate, including the product, wasthen evaporated to dryness and heated under vacuum to remove anyresidual naphthalene contained in the crude product. The recoveredproduct weighed 27.34 g resulting in a calculated reaction efficiency ofabout 77%. The composition of the product was verified to be Te(SiMe₂^(t)Bu)₂ by nuclear magnetic resonance (NMR), mass spectroscopy (MS) andsingle crystal x-ray diffraction. The Te(SiMe₂ ^(t)Bu)₂ produced was asolid with a melting point of 44° C.

Example 15

Te(SiEt₃)₂ was produced by a process similar to that described inExample 14. First, 0.23 g of lithium was added to 300 ml of dry THFalong with 2.12 g of Te powder and 0.3 g of naphthalene in a 600 mlSchlenk bottle. The resultant mixture was heated and a reflux condenserwas mounted on the bottle. The solution was refluxed with an argonatmosphere. Solution was initially colorless with undissolved solid Liand Te. During, the reflux period the mixture turned a violet color andthen back to a clear solution with a white precipitate. After the whiteprecipitate was formed, the solution was cooled to 0° C.

Next, 5.0 g of Et₃SiCl was added to the mixture. The mixture wasconstantly stirred at room temperature over night. The final product wasisolated from the other reactants and any by-products. The recoveredproduct weighed 4.8 g resulting in a reaction efficiency of about 80%.The composition of the product was verified to be Te(SiEt₃)₂ by nuclearmagnetic resonance (NMR) and mass spectroscopy (MS). The compound was abrownish liquid at room temperature.

It will be appreciated by those skilled in the art that variousmodifications and changes can be made without departing from the scopeof the invention. Similar other modifications and changes are intendedto fall within the scope of the invention, as defined by the appendedclaims.

We claim:
 1. A process for making a Te or Se precursor, comprising: forming a first product by reacting an elemental Group IA metal with a material comprising Te or Se; and subsequently adding a second reactant comprising a silicon atom bound to a halogen atom, wherein the second reactant is selected from the group consisting of Et₃SiCl, Me₃SiCl, [R¹R²R³Si]₃—Si—X, [R¹R²N]₃—Si—X, [R¹—O]₃—Si—X, R¹R²SiX with a double bond between silicon and one of the R groups, and X—Si—R—Si—X, wherein R¹, R² and R³ are alkyl groups with one or more carbon atoms and X is a halogen, thereby forming one of (Et₃Si)₂Te, (Me₃Si)₂Te, Te(SiMe₂ ^(t)Bu)₂, (Et₃Si)₂Se, (Me₃Si)₂Se, or Se(SiMe₂ ^(t)Bu)₂.
 2. The method of claim 1, wherein forming a first product comprises using THF as a solvent.
 3. The method of claim 1, wherein the second reactant is Et₃SiCl and Te(SiEt₃)₂ is formed.
 4. The method of claim 1, wherein the second reactant is Me₃SiCl and Te(SiMe₃)₂ is formed.
 5. The method of claim 1, wherein the Group IA metal is Li.
 6. The method of claim 1, wherein the material comprising Te or Se is elemental Te or Se.
 7. The method of claim 1, wherein forming a first product includes using naphthalene as a catalyst.
 8. The method of claim 1, wherein the Group IA metal is in the form of a powder or flakes.
 9. The method of claim 1, wherein the material comprising Te or Se is elemental Te.
 10. The method of claim 9, wherein the elemental Te is provided in the form of a powder.
 11. The method of claim 1, wherein the material comprising Te or Se is elemental Se.
 12. The method of claim 11, wherein the elemental Se is provided in the form of a powder.
 13. A process for synthesizing (Et₃Si)₂Te, (Me₃Si)₂Te, Te(SiMe₂tBu)₂, (Et₃Si)₂Se, (Me₃Si)₂Se, or Se(SiMe₂tBu)₂ comprising: forming a first product by reacting a first reactant that is an elemental Group IA metal with a second reactant comprising Te or Se, wherein forming comprises adding naphtalene to a mixture of the first reactant and the second reactant; and subsequently adding a third reactant comprising a silicon atom bound to a halogen atom, wherein the third reactant comprises R¹R²R³SiX, wherein R¹, R² and R³ are alkyl groups with one or more carbon atoms and X is a halogen, thereby forming (Et₃Si)₂Te, (Me₃Si)₂Te, Te(SiMe₂tBu)₂, (Et₃Si)₂Se, (Me₃Si)₂Se, or Se(SiMe₂tBu)₂.
 14. The method of claim 13 wherein forming a first product includes using THF as a solvent.
 15. The method of claim 13, wherein the third reactant is Et₃SiCl and (Et₃Si)₂Te is formed.
 16. The method of claim 13, wherein the third reactant is Me₃SiCl and (Me₃Si)₂Te is formed.
 17. The method of claim 13, wherein the elemental Group IA metal is Li.
 18. The method of claim 13, wherein the elemental Group IA metal is in the form of a powder or flakes.
 19. The method of claim 13, wherein the second reactant is elemental Te or Se.
 20. The method of claim 19, wherein the elemental Te or Se is provided as a powder. 